Oxygen Carriers: Kinetic Analysis
CaSO4 has the largest oxygen carrying capacity among all the currently proposed carriers. The oxygen ratio is 0.4706 for CaSO4-calcium sulphide (CaS), much higher than that of many other metal oxides such as CuO-Cu2O, NiO-Ni, and Fe2O3- Fe3O4. Calcium sulphate is a relatively stable material. It is a widespread natural resource and therefore the cost would be quite low even if the demand is high.
Through the thermodynamic analysis, it seemed that CaSO4 can be used as a promising oxygen carrier for chemical looping combustion.
High heating rate leads to the increase of the initial reacting temperature. The initial reaction starts from 830 ℃ with heating rate of 5 ℃ /min, 930℃ with heating rate of 20 ℃ /min.
Kinetic parameters of reductive …show more content…
But no substantial connection was found between the lowered peak temperatures and ratio of SiO2 added. The reaction rate (such as Rmax) is increased during fuel gas-CaSO4 reaction.
The addition of SiO2 as a binder promoted the conversion of solid reactant (CaSO4) in the reaction with fuel gas at relatively low temperatures. The maximum reaction rates (Rmax) of pure CaSO4 with CH4, CO, and H2 were 1.97×10-4, 5.01×10-4, and 1.04×10-3 s-1 at 840 ℃, which was considerably lower than the value 1.37 ×10-3 s-1 of CuO-based oxygen carrier at 850 ℃. But for 13.5 wt % SiO2-supported CaSO4, the value of Rmax increased to 1.24 ×10-3, 9.91× 10-3, and 3.95 ×10-3 s-1, respectively.
The addition of SiO2 as a binder also promoted the conversion of solid reactant (CaSO4) in the reaction with fuel gas at relatively low temperatures.
The maximum conversion (Xmax) of CaSO4 was limited to 27.24%, 54.45%, and 89.12%, respectively, for CH4, CO, and H2. When 13.5 wt % SiO2-supported CaSO4 was used, Xmax increased and became 90.87%, 94.50%, and 100%, respectively. This indicates that SiO2-supported oxygen carriers can be used at lower operating temperatures, avoiding the decomposition of oxygen carriers with the release of